Geology of building stones – identify the volcanic (extrusive igneous) rock Which one of the following is a volcanic rock?

Introduction:
Construction materials often originate from different geological processes. Knowing whether a stone is volcanic (extrusive), plutonic (intrusive), or hypabyssal (shallow intrusive) helps predict texture, strength, durability, and typical uses in civil engineering.

Given Data / Assumptions:

• Options: Granite, Dolerite, Basalt, All of the above.
• “Volcanic” implies extrusive igneous rocks formed at or near the surface from lava.

Concept / Approach:

Igneous rocks are classified by where they solidify. Extrusive (volcanic) rocks cool quickly at the surface, producing fine-grained textures (e.g., basalt, rhyolite). Intrusive (plutonic) rocks cool slowly at depth, forming coarse-grained textures (e.g., granite). Hypabyssal rocks cool at shallow depths with intermediate texture (e.g., dolerite/diabase).

Step-by-Step Solution:

Verification / Alternative check:

Basalt forms from low-viscosity mafic lava flows, a hallmark of volcanic provinces (e.g., Deccan Traps). Granite, in contrast, crystallizes deep within the crust, giving large feldspar and quartz crystals; dolerite commonly occurs in dykes and sills with medium grains.

Why Other Options Are Wrong:

Granite: Intrusive, not extrusive; coarse grains indicate slow deep cooling.
Dolerite: Hypabyssal; neither deep intrusive nor extrusive; thus not volcanic in the strict sense.
All of the above: False because only basalt is volcanic.

Common Pitfalls:

Assuming any igneous rock is “volcanic.” The term volcanic specifically refers to extrusive rocks like basalt, pumice, and rhyolite.

Final Answer:

Basalt